Radar protection device for wireless networks

ABSTRACT

A method for radar protection. The method includes recording energy events and calculating differences in recorded energy events to determine pulses. The method further includes sorting intervals between pulses into histogram bins, each bin representing a range of time intervals between two pulses, each pulse indicative of a radar frequency and limiting network traffic on a frequency based on a selected bin count.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application No.10/910,682, filed on Aug. 3, 2004.

BACKGROUND

Current and projected growth for unlicensed wireless devices operatingin a frequency band located at approximately 5 Gigahertz has promptednational and international regulatory bodies to promulgate regulationsthat ensure that interference with incumbent systems is minimized. Suchunlicensed wireless devices generally use packeted data and include, butare not limited to, wireless devices in accordance with the Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard. More oftenthan not, such regulations are, in part, due to military and weatherradar operations ordinarily conducted within the band. Generally, theoperation of more unlicensed devices within the band increases theopportunity for interference and raises the noise floor of the band,potentially compromising the operational performance of military andweather radar systems.

For instance, both the European Telecommunications Standards Institute(ETSI) and the Federal Communications Commission (FCC) have publishedrequirements for radio local area network (RLAN) devices that operate inthe Unlicensed National Information Infrastructure (U-NII) frequencybands between 5.250-5.350 and 5.470-5.725 Gigahertz. Further, thedevices are required to employ a mechanism that allows the devices toshare the spectrum with radar operations, notably military and weatherradar operations, in such a way that the devices do not interfere withradar operations.

Short of the required sharing of the spectrum, one approach reports ameasurement summary in a radio communications system. More specifically,once a mobile station within a system is tuned to a selected frequencyrange, a measurement is made of communications energy. If communicationsenergy is measured or detected, the energy is decoded to determinewhether the communications energy contains packeted data. If packeteddata is detected, further analysis of the data packet is conducted todetermine whether the packeted data is in accordance with the Instituteof Electrical and Electronics Engineers (IEEE) 802.11 standard. If it isdetermined that the packeted data is 802.11 packeted data, a measurementsummary field is populated with a value indicating the frequency rangeto which the mobile station is tuned. Otherwise, an indication is madethat 802.11 packeted data is not being communicated on the frequencyrange to which the mobile station is tuned. The approach uses a rathercomplex delay correlation method for such determinations. Although thisapproach reports a measurement summary for a mobile station inclusive ofwhether or not communicated energy on a particular frequency is 802.11packeted data, the approach fails to provide a radar protection systemfor wireless devices that allows the co-existence of a wireless networkwith radar systems.

However, another approach does allow the co-existence of a wirelessnetwork with radar systems. More specifically, this approach providesradar detection and dynamic frequency selection for wireless local areanetworks. Further, this approach includes a radar detection process thatperforms a frequency domain analysis of an incoming signal to derivephase and magnitude information, the output of which is binned into 52bins of 300 kilohertz. The bins are analyzed to identify and distinguishamong different types of radar such as continuous wave tone radar andchirping radar in which the pulses are swept across a frequency range.With radar, the power is typically concentrated in one of the bins, orat a specific frequency.

This approach also provides analysis of a packet to determine whetherthere are any spikes within the packet above a certain threshold, as aspike might indicate a radar signal. The amplitude and duration, i.e.,pulse width, of the spike is analyzed to determine whether or not thespike is indicative of a radar signal. Spikes within the packet may betime-stamped so that the spike can be treated as a new or separateevent.

This approach also determines the period of a signal once a particularevent is determined to be a radar signal through a frequency domainanalysis of the length and magnitude of the event. Similarly, afrequency domain analysis is used to determine the period of a signal.

Particularly, this approach uses the forgoing radar detection process atan access point, and if the access point detects the presence of a radarsignal, the access point changes channels. Despite providing a radarprotection system for wireless devices that allows the co-existence of awireless network with radar systems, the radar detection processassociated with this approach is of limited utility. Foremost, the useof Fast Fourier Transform, Discrete Fourier Transform, or time domainanalysis is particularly burdensome. All of these types of analysisrequire significant computational and processing capabilities. Moreover,such processing can take a considerable amount of time. Further,capabilities inherent in current access points are generallyinsufficient to allow the use of such types of analysis. Therefore, manyexisting access points are not capable of using analysis processesassociated with this approach.

OVERVIEW OF EXAMPLE EMBODIMENTS

In an example embodiment, there is disclosed herein an apparatus thataddresses regulatory requirements and allows the co-existence of awireless network with radar systems. The apparatus scans for thepresence of radar signals and, upon detection, limits transmissions ofthe wireless network device on the same frequency, thereby reducinginterference with and protecting the operation of radar systems.

In an example embodiment, there is disclosed herein an apparatuscomprising a circuit for receiving a wireless signal, and a processorcoupled to the circuit and operable to select an operating frequency forthe circuit. The processor is configured to record energy eventsreceived by the receiver. The processor is responsive to recording theenergy events to determine temporal differences between the energyevents. The process is responsive to determining temporal differencesbetween the energy events to maintain a count of temporal differencesfor a range of time intervals. The processor is responsive to select anew operating frequency responsive to the count of temporal differencesfor the range of time intervals exceeding a predetermined threshold.

In an example embodiment, there is disclosed herein a method comprisingrecording energy events on a first frequency and calculating temporaldifferences between the record energy events. A count of temporaldifferences for a range of time intervals is maintained. A secondfrequency is selected responsive to the count of temporal differencesfor the range of time intervals exceeding a predetermined threshold.

By virtue of the foregoing, there is thus provided a radar protectiondevice and method that addresses the regulatory requirements and allowsthe co-existence of a wireless network with radar systems.

These and other objects and advantages of the present invention willbecome readily apparent to those skilled in this art from the followingdescription wherein there is shown and described a preferred embodimentof this invention, simply by way of illustration of one of the bestmodes suited to carry out the invention. As it will be realized, theinvention is capable of other different embodiments and its severaldetails are capable of modifications in various obvious aspects allwithout departing from the spirit of the present invention. Accordingly,the drawings and descriptions will be regarded as illustrative in natureand not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description given below, serve to explainthe principles of the present invention.

FIG. 1 illustrates an example of a functional block diagram of a portionof an access point configured in accordance with an example embodiment.

FIG. 2 illustrates an example graphical depiction of a signal indicatingthe operation of the access point shown in FIG. 2.

FIG. 3 is an example temporal plot of the operation of the access pointshown in FIG. 2.

FIG. 4 illustrates an example histogram of the pulse intervals shown inFIG. 4.

FIG. 5 illustrates an example of a functional block diagram of an accesspoint in accordance with principles of the present invention.

FIG. 6 illustrates an example computer system for implementing anexample embodiment.

FIG. 7 illustrates an example embodiment of a wireless local areanetwork including a number of access points configured to detect a radarsignal.

FIG. 8 is flowchart illustrating an example program flow of a method fora radar protection.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Radar signals are characterized by bursts of periodic pulses of radiofrequency energy. These pulses are distinguishable from wireless networktransmissions due to their periodicity and relatively short pulse width.The number of pulses and the period of time between the pulses vary fordifferent types of radar. Despite this variation, the number of pulsesand the period of time between the pulses may be parameterized. Forexample a radar signal may comprise a series of pulses received in aseries of bursts. Bursts are separated by a period of time generallyindicated at reference numeral. The period of time between the start ofconsecutive pulses is referred to as the pulse period and is the inverseof the pulse repetition frequency (PRF), designated as (1/PRF). Theburst length (BL) is the number of pulses in a burst or, equivalently,the time taken for a burst of pulses. The burst interval (P) is the timetaken between two equivalent reference points in two consecutive burstsand typically is between approximately 1-60 seconds.

Thus, a radar signal is characterized by periodic pulses and periodicbursts and is parameterized accordingly. It will be appreciated by theskilled artisan that the aforementioned radar signal is an example of arotating radar signal and that a tracking radar signal will not appearas periodic busts. However, the techniques described herein also applyto tracking radar signals using the periodicity between pulses.

Referring to FIG. 1, there is illustrated a block diagram of a receiverportion of an access point 300, configured in accordance with an exampleembodiment is shown. Access point 300 includes a receive antenna 302coupled to a bandpass filter 304 and a low noise amplifier 306, forreceiving packeted data on a reverse link channel. Access point 300further includes a mixer 308 and an associated local oscillator 310responsive to a controller 324, coupled to low noise amplifier 306 fortuning to or selecting a receive frequency or channel. A series ofbandpass filters 312, 316 and amplifiers 314, 318 are coupled to mixer308 and analog-to-digital converter 322, and complete a receive path338. In accordance with an example embodiment, receive path 338 is usedto detect radar signals.

Access point 300 further comprises an 802.11 physical layer interfacecontroller (PHY) 334. Physical layer interface controller 334 comprisesanalog-to-digital converters 322, 332, controller 324, blanking 326,gating 328, and detection and timestamping 330.

In operation, referring to connections 336, the power supply currents ofamplifiers 306, 314, and 318 are integrated and coupled toanalog-to-digital converter 332. The integration of the power supplycurrents form received signal strength indication (RSSI) signals. Inaccordance with an example embodiment, one or more received signalstrength indication signals are used over time to detect radar. Morespecifically, when receive path 338 receives a signal, and a receivedsignal strength indication signal greater than a threshold, for example,greater than −64 dBm, is indicated, detection and timestamping 330stores or records the event in memory. For example, the event in memorycan be stored as four consecutive 16-bit words. Further, the lower twowords can record information as to the type of event, along with otherinformation, while the upper two words are an actual 32-bit (rollover)timer count at the time of the event. Controller 324 is operational toprocess events stored or recorded in memory to detect radar as will bedescribed hereinafter. Blanking 326 and gating 328 is used for timeswhen is either transmitting or receiving packet data such thattransmitted and received packeted data is not recorded.

In an example embodiment, energy events received on receive path 338 aresuitably recorded controller 334. In an example embodiment, energyevents having an energy level rising above a specified threshold and anenergy level falling below the specified threshold are recorded.Temporal differences in the recorded energy events are calculated todetermine the presence of pulses. For example, the difference intime-stamps between corresponding portions (e.g., leading edges) ofpulses is used to calculate intervals between pulses. In an exampleembodiment, intervals between pulses that fall outside a range, e.g.,either too narrow or too wide, are discarded as such intervals are notgenerally indicative of a radar signal.

The intervals between pulses are sorted into a histogram including anumber of bins. Each bin of the histogram represents a range of timeintervals between two pulses. FIG. 4 shows an example histogram 600.Accumulations in a single bin of the histogram represent intervals thathave a periodicity within a margin of error equal to the range of thebin.

In an example embodiment, the histogram is periodically reset, i.e., allaccumulations in any bins of the histogram are discarded. For example,all of the bins are suitably reset once approximately every one hundredmilliseconds. Alternatively, the oldest entries in the bins are purged,such as those older than, for example, 750 milliseconds. If any bin ofthe histogram exceeds a specified bins count, this indicates thepresence of a number of similarly spaced pulses correlating to a highprobability that a radar signal has been received. Generally,periodically resetting or purging old entries from the bins preventsfalse detections of radar signals.

When a bin count in the histogram provides an indication of radardetection, transmission of interfering wireless network traffic islimited or ceased on any frequency where a potential radar signal isdetected, thereby reducing or eliminating interference with the radarsystem. To distinguish radar system transmissions from random highfrequency pulses, wireless network traffic is ceased when themeasurement intervals between pulses are concentrated in a small numberof histogram bins, and thusly, uncorrelated detection is isolated fromcorrelated binning due to radar periodicity.

Referring to FIG. 2 with continued reference to FIG. 1, there isillustrated a depiction of an example signal 400 received by accesspoint 300 (shown in FIG. 1). In an example embodiment, access point 300is generally capable of receiving signals ranging in magnitude betweenapproximately −94 and −20 dBm, as generally indicated on the ordinate ory-axis. Signals greater than −20 dBm typically overdrive or saturate thereceive path 338 of access point 300. Time is generally indicated on theabscissa or x-axis. Those of ordinary skill in the art will appreciatethat the radar detection technique described herein applies equally wellto receivers having differing receive sensitivities.

As mentioned, signal 400 includes portions 402, 404 in which an accesspoint associated with access point 300 is transmitting and receivingpacketed data, respectively. It will be appreciated that portions orpackets 402, 404 need not have amplitudes equaling −64 dBm; rather, thisamplitude was merely for convenience and purposes of illustration.Transmitted and received packet data is generally between approximately24 microseconds and 1.5 milliseconds in duration. Thus, in an exampleembodiment receive path 338 is effectively blanked during periods 402,404. It will be appreciated that, in some embodiments, much of the samereceive path 338 is used for both radar detection and packet reception.In these embodiments, only the radar detection path is blanked while theaccess point receives packets.

It will be appreciated that access point 300 includes accommodations fordistributed coordinate function interframe space (DIFS) and randombackoff; in which case, the periods for transmitting and receivingpacketed data vary. Further, access point 300 can include accommodationsfor a “quiet period” before, during, or after the transmission of eachpacket.

Between transmitting and receiving packeted data, access point 300“listens” for signals, such as radar signals, during clear channelassessment (CCA) using receive path 338. Example periods for listeningor clear channel assessment are generally indicated at referencenumerals 406 and 408, while a detected radar spike or signal isindicated at reference numeral 410. Typically, a radar signal 410 is apulse of approximately 4 microseconds in duration; however, pulses aslong as hundreds of microseconds are known.

In order for a radar signal to be detected, the signal exceeds athreshold. For example, radar signal 410 exceeds a threshold, forexample −64 dBm, as generally indicated by arrows 412 and 414. Those ofordinary skill in the art will appreciated that such a threshold can beset to any appropriate power level as desired.

Referring to FIG. 3, with continued reference to FIG. 1, there isillustrated a temporal plot 500 of the operation of an access pointassociated with access point 300 shown in FIG. 1. Generally, time isindicated on the abscissa or x-axis and power or magnitude is indicatedon the ordinate or y-axis. More specifically, temporal plot 500 showstransmitted and received packeted data 502, 504, respectively, and aseries of periodic radar bursts or pulses 506, 508, 510, 512, 514, etc.As shown in dashed line at reference numeral 516, radar pulses 506, 508,510, 512, 514, etc. are subject to some “jitter” or variation in time.In accordance with an example embodiment, such jitter is allowed for inthe detection of radar through “binning” as will be shown hereinafter.

In detecting a radar signal, received signal strength indication eventsduring the transmission or reception of packeted data are ignored.Further, pulses that are either too narrow or too wide are ignored, asare pulses with too much width variation. An example pulse that iseither too narrow or too wide or has too much width variation is shownat reference numeral 518. Thus, transmitted and received packeted data502, 504 and example pulse 518 are eliminated from spectrogram 500. Itwill be appreciated that radar pulse 512 is also effectively eliminatedalong with received packeted data 504. As will be shown hereinafter,despite eliminating radar pulse 512, an example embodiment disclosedherein is still capable of detection the operation of a radar system.

Once transmitted and received packeted data 502, 504, pulse 512, andexample pulse 518 are eliminated, the intervals between radar pulses506, 508, 510, 514, etc. are designated as A1, A2, B, and A3,respectively. It will be appreciated that intervals A1, A2, and A3 aresimilar, while interval B is longer due to the elimination of pulse 512with packeted data 504. In an example embodiment, intervals betweenpulses that are either too narrow or too wide are discarded; as suchintervals are not generally indicative of a radar signal.

Referring to FIG. 4, a histogram 600 is built in memory using theintervals. Such a memory is advantageously included in applicationspecific integrated circuit 334 or as part of controller 324, both ofwhich are shown in FIG. 1. In other embodiments, a memory external to anapplication specific integrated circuit or a controller can be used.

More specifically, histogram 600 includes a plurality of bins, e.g.,bins 602, 604, denoting the interval between two pulses arranged alongthe abscissa or x-axis. Bins 602, 604 generally cover a range ofintervals such as, for example, 200-250 microseconds and 400-500microseconds, respectively. The number of occurrences, e.g., a “bincount”, of an interval between two pulses falling in a range isindicated on the ordinate or y-axis. Those of ordinary skill in the artwill appreciate that any number of bins having any desired ranges may beused.

As shown, intervals A1, A2, B, A3 have been binned. Thus, bin 602contains intervals A1, A2, and A3, and bin 604 contains interval B. Oncethe count within one or more bins 602 exceeds are particular bin count606, access point 300 discontinues use of that frequency or channelassociated with those pulses and engages in dynamic frequency selection(DFS), thereby utilizing another available channel. Those of ordinaryskill in the art will appreciate that a bin count 606 may be adjusted asdesired to change when or how quickly a radar signal is detected.

For example, one criterion that can be used to detect a radar signal isthat if less than a particular number of bins are populated withintervals and if any of the bin counts are greater than some number,dynamic frequency selection is engaged. Such a criterion prevents falsedetections of radar. It has been found that if closely spaced bins haverespective bin counts that follow a Gaussian distribution, a radarsignal is not present; but rather, the access point 300 is detecting itsown transmissions. Thus, closely spaced bins having bin counts thatfollow a Gaussian distribution should be ignored. In such an instance,the bins 602, 604, should purged, reset, or cleared. Similarly, the bins602, 604 can be cleared periodically or once a radar signal has beendetected.

Referring to FIG. 7, a functional block diagram of an access point 700in accordance with an example embodiment is shown. More specifically,access point 700 includes a receive path 702 for receiving packeted dataon a reverse link channel and a transmit path 704 for transmittingpacketed data on a forward link channel. Receive path 702 comprisesantenna 706, low noise amplifier 708, frequency conversion process 710,analog-to-digital (A/D) converter 712, and physical interface (PHY)controller 714. Receive path 702 further comprises an automatic gaincontrol (AGC) circuit 716 providing receive signal strength feedbacksignals. Similarly, transmit path 704 comprises physical layer interfacecontroller 714, digital-to-analog (D/A) converter 718, frequencyconversion process 720, power amplifier 722, and antenna 724. Physicallayer interface controller 714 selects between receive path 702 andtransmit path 704 using switches 726, 728, as indicated at referencenumeral 730. A local oscillator 732 is used to select transmit andreceive channels.

Physical layer interface controller 714 is, in an example embodiment,advantageously an application specific integrated circuit that runs offof a clock, such as, for example, a 40 Megahertz clock (not shown). Inother embodiments, physical layer interface controller 714 can includeanalog-to-digital converter 712 and digital-to-analog converter 718.Further, physical layer interface controller 714 performsmodulation/demodulation.

Physical layer interface controller 714 is coupled to media accesscontroller (MAC) 734, processor 736 that is coupled to network 738.Media access controller 734, in an example embodiment, is likewiseadvantageously an application specific integrated circuit. Network 738is a distribution network (e.g. a backbone network), such as network 106that will be described herein in FIG. 6.

Processor 736 controls functions of access point 700, such as, forexample, transmissions and receptions associated with a wireless link.Processor 736 is coupled to receive and transmit paths 702, 704 andlocal oscillator 732 and executes stored program code found in memory740. Processor 736 is thus programmed to record and/or manage detectedradar signals and to select communications channels for transmissions onforward, and by inference client return, links to prevent interferencewith radar systems in various ways depending upon its stored programcode. As will be appreciated by those of ordinary skill in the art, aprocessor suitably includes a memory in alternative embodiments. In yetother embodiments, a memory is external to or not a part of access point700. Processor 736 detects a radar signal by recording energy events,calculating temporal differences in recorded energy events to determinethe presence of pulses, sorting intervals between pulses into histogrambins, each bin representing a range of time intervals between twopulses, each pulse indicative of a radar frequency, and limiting networktraffic on a radar frequency based on a selected bin count.

FIG. 6 illustrates an example of a wireless local area network (WLAN)100 configured to provide wireless data communications with a mobilestation 102 and is operable to provide radar detection. In an exampleembodiment, wireless local area network 100 and mobile station 102operate in accordance with the Institute of Electrical and ElectronicsEngineers (IEEE) 802.11 standard in a frequency band located atapproximately 5 Gigahertz. In an example embodiment, wireless local areanetwork 100 operates in accordance with requirements published by theEuropean Telecommunications Standards Institute (ETSI) and the FederalCommunications Commission (FCC) for unlicensed wireless devices thatoperate in the Unlicensed National Information Infrastructure (U-NII)frequency bands between 5.250-5.350 and 5.470-5.725 Gigahertz.

Further, wireless local area network 100 includes a radar protectiondevice that allows the network to share the spectrum with radaroperations, e.g., military and weather radar operations, in such a waythat the network does not interfere with the radar operations. Radardetection may be performed at a centralized location, or may beperformed by access points 104 a-n, where “n” denotes any practicalnumber of access points. Access points 104 a-n are advantageouslyinterconnected by network 106. As shown and in operation, packeted datais communicated using a wireless link 108 between mobile station 102 anda selected access point 104 a. Packeted data transmitted by access point104 a to mobile station 102 using wireless link 108 is transmitted onwhat is commonly referred to as a forward link channel, while packeteddata transmitted by mobile station 102 to access point 104 a istransmitted on what is commonly referred to as a reverse link channel.

Those of ordinary skill in the art will appreciate that access points104 a-n can also advantageously be dedicated to or used as a bridge. Ina bridge application or configuration, an access point 104 a-n isprimarily dedicated to wirelessly communicating with another accesspoint. In such a configuration, an access point 104 a-n typically uses adirectional antenna aimed or pointed at the other access point toprovide additional gain and selectivity. An access point 104 a-nconfigured as a bridge generally does not communicate with a mobilestation 102. Thus, the example embodiment is not limited to accesspoints 104 a-n that communicate with mobile stations; but rather,includes access points configured as bridges or any other wirelessdevice.

In the Unlicensed National Information Infrastructure (U-NII) frequencybands frequency bands between 5.250-5.350 and 5.470-5.725 Gigahertz,forward and reverse link channels are not assigned to particularsystems. In other words, wireless local area network 100 is not assigneda portion of the frequency band(s) for its exclusive use. Rather,wireless local area network 100 must share the frequency band(s) withother concurrently operated systems, notably radar systems. Radarsystems include, but are not limited to, military and weather radarsystems ordinarily operated within the band(s), an example radar systembeing shown at reference numeral 110. To prevent simultaneous usage ofthe same portion of the frequency band(s), a dynamic frequency selectionscheme is to be utilized by a system operating within the band(s)according to current published requirements by both the FederalCommunications Commission and the European Telecommunications StandardsInstitute.

Generally speaking, in a dynamic frequency selection scheme, channelswithin the band(s) are dynamically selected for use based upon whetheror not the channel is being used by another system. More specificallyand in accordance with an example embodiment, if a channel is being usedby a radar system, e.g., radar system 110, access points 104 a-n selectanother channel for data communications. Furthermore, when using adynamic frequency selection scheme in accordance with teachings herein,this avoids using the same channel by both a radar system 110 and awireless local area network 100.

In an example embodiment, access points 104 a-n are configured toprovide radar protection as described herein. In an example embodiment,each access point 104 a-n records energy events. This enables eachaccess point to independently detect potential radar signals. In largenetworks, it is possible that only a subset of access points are withinrange of a radar, and the remaining access points can operate withoutinterfering with the radar. For example, as illustrated in FIG. 6, radarsystem 110 is in close proximity to access points 104 a, 104 b, and 104n. Each of access points 104 a, 104 b and 104 n can independently detectradar signals from radar system 100 and responsive to detecting radarsignals from radar system 100 change operating frequencies to preventinterfering with radar system 110. In an example embodiment, accesspoint 104 c is sufficiently far enough away from radar system 110,enabling access point 104 c to operate on a frequency that isunavailable to access points 104 a, 104 b and 104 n

In view of the foregoing structural and functional features describedabove, methodologies in accordance with various aspects of the presentinvention will be better appreciated with reference to FIG. 7. While,for purposes of simplicity of explanation, the methodology of FIG. 7 isshown and described as executing serially, it is to be understood andappreciated that the present invention is not limited by the illustratedorder, as some aspects could, in accordance with the present invention,occur in different orders and/or concurrently with other aspects fromthat shown and described herein. Moreover, not all illustrated featuresmay be required to implement a methodology in accordance with an aspectof the present invention. In addition, methodologies of the presentinvention can be implemented in software, hardware, or a combination ofsoftware and hardware.

Referring now to FIG. 7, a flowchart illustrating the program flow of amethod 800 for a radar protection device for wireless networks is shown.The method 800 begins by recording, e.g., detecting, timestamping and/orlogging, energy events in block 802. As used herein, energy eventsinclude, among other things, transmissions from radar systems, such asradar system 110 shown in FIG. 6.

For example, energy events are suitably recorded by receive path 338responsive to controller 334, shown in FIG. 1 or receive path 702responsive to processor 736, shown in FIG. 5. More specifically, energyevents having an energy level rising above a specified threshold and anenergy level falling below the specified threshold are recorded. Suchrising and falling events above and below a specified thresholdcorrespond to the leading and trailing edges of pulses. Similarly, aradar signal 410 exceeding a threshold of −64 dBm, as generallyindicated by arrows 412 and 414, is shown in FIG. 2.

Still referring to FIG. 7 and at block 804, temporal differences in therecorded energy events are calculated to determine the presence ofpulses. For example, the difference in time-stamps between correspondingportions, e.g., leading edges, of pulses 506, 508, 510, 514, etc. areused to calculate intervals A1, A2, B, A3, as shown in FIG. 3. At block806, intervals between pulses that fall outside a range, e.g., eithertoo narrow or too wide, are discarded as such intervals are notgenerally indicative of a radar signal.

At block 808, the intervals between pulses are sorted into a histogramincluding a number of bins. Each bin of the histogram represents a rangeof time intervals between two pulses. FIG. 4 shows an example histogram600. Accumulations in a single bin of the histogram represent intervalsthat have a periodicity within a margin of error equal to the range ofthe bin.

At block 810, the histogram is periodically reset, i.e., allaccumulations in any bins of the histogram are discarded. For example,all of the bins are suitably reset once approximately every one hundredmilliseconds. Alternatively, the oldest entries in the bins are purged,such as those older than, for example, 750 milliseconds. Any bin of thehistogram exceeding a specified bins count, e.g., bin count 606, shownin FIG. 4, within the reset period indicates the presence of a number ofsimilarly spaced pulses correlating to a high probability that a radarsignal has been received. Generally, periodically resetting or purgingold entries from the bins prevents false detections of radar signals.

At block 812, and using the bin count in the histogram as an indicationof radar detection, transmission of interfering wireless network trafficis limited or ceased on the frequency that is detected, thereby reducingor eliminating interference with the radar system. To distinguish radarsystem transmissions from random high frequency pulses, wireless networktraffic is ceased when the measurement intervals between pulses areconcentrated in a small number of histogram bins, and thusly,uncorrelated detection is isolated from correlated binning due to radarperiodicity. The method 800 ends in block 814.

In order for a wireless network to successfully share the spectrum withradar systems, a radar signal must be detected quickly, efficiently, andaccurately. The foregoing method uses relatively lower computationalprocessing when compared with methods that use Fourier or PeriodicTransforms, and results in high detection rates and low false alarmrates. Further, the foregoing method is robust in the presence ofuncorrelated detection noise and is easily parameterized to account fordifferences in radar systems.

By virtue of the foregoing, there is thus provided a radar protectiondevice and method that addresses the regulatory requirements and allowsthe co-existence of a wireless network with radar systems.

While the present system has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. It will be understood that the presentinvention is applicable to any wireless network using packeted data.Moreover, such a network is not limited to operation in any particularfrequency band; but rather, may operate at any frequency as desired.Further, the invention is not limited to operation in accordance withany standard or regulations. Therefore, the invention, in its broaderaspects, is not limited to the specific details, the representativeapparatus, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

1. An apparatus, comprising: a circuit for receiving a wireless signal;and a processor coupled to the circuit and operable to select anoperating frequency for the circuit; wherein the processor is configuredto record energy events received by the receiver; wherein the processoris responsive to recording the energy events to determine temporaldifferences between the energy events; wherein the process is responsiveto determining temporal differences between the energy events tomaintain a count of temporal differences for a range of time intervals;and wherein the processor is responsive to select a new operatingfrequency responsive to the count of temporal differences for the rangeof time intervals exceeding a predetermined threshold.
 2. An apparatusaccording to claim 1, further comprising the processor is configured torecord energy events having an energy level rising above a specifiedthreshold and an energy level falling below the specified threshold arerecorded.
 3. An apparatus according to claim 1, wherein the recordingenergy events by the processor includes at least one of detecting,time-stamping, and logging energy events.
 4. An apparatus according toclaim 1, wherein the recorded energy events are pulses having a widthwithin a desired range.
 5. An apparatus according to claim 4, whereinthe desired range is approximately one to twenty microseconds.
 6. Anapparatus according to claim 1, further comprising the processor isconfigured to periodically reset the count.
 7. An apparatus according toclaim 6, wherein the count is reset once approximately every one hundredmilliseconds.
 8. An apparatus according to claim 1, further comprisingthe processor is configured to periodically purge the oldest energyevents.
 9. An apparatus according to claim 8, wherein energy eventsolder than approximately 750 milliseconds are purged.
 10. An apparatusaccording to claim 1, further comprising: a transmitter coupled to theprocessor; wherein the processor is operable to select an operatingfrequency for the transmitter; and wherein the processor is responsiveto select a new operating frequency for the transmitter responsive tothe count of temporal differences for the range of time intervalsexceeding a predetermined threshold.
 11. An apparatus according to claim10, further comprising a blanking and gating circuit configured todetect packeted data received by the receiver and packeted data sent bythe transmitter, wherein the processor is configured not to recordpacketed data received by the receiver and packeted data sent by thetransmitter as energy events.
 12. An apparatus according to claim 1,further comprising the processor is configured to maintain a pluralityof counts of temporal differences corresponding to a plurality of rangesof time intervals, wherein the processor is responsive to selecting anew operating frequency responsive to a one of the plurality of countsexceeding the predetermined threshold.
 13. An apparatus according toclaim 1, wherein the recorded energy events are energy events determinednot to contain packeted data.
 14. An apparatus according to claim 1,wherein the recorded energy events have an energy level rising above aspecified threshold and an energy level falling below the specifiedthreshold.
 15. A method, comprising: recording energy events on a firstfrequency; calculating temporal differences between record energyevents; maintaining a count of temporal differences for a range of timeintervals; and selecting a second frequency responsive to the count oftemporal differences for the range of time intervals exceeding apredetermined threshold.
 16. A method according to claim 15, wherein therecorded energy events are energy events determined not to containpacketed data.
 17. A method according to claim 15, wherein recordingenergy events comprises one of a group consisting of detecting energyevents, time-stamping energy events, and logging energy events.
 18. Amethod according to claim 15, wherein the recorded energy events have apulse width within a predetermined range.
 19. A method according toclaim 15, further comprising resetting the count after a predeterminedtime interval.
 20. A method according to claim 15, further comprisingmaintaining a plurality of counts corresponding to a plurality of timeintervals, wherein the selecting the second frequency responsive to aone of the plurality of counts exceeding a predetermined threshold.